2002 cooper s went to start car it wouldn’t turn over just clicked so I push started it drove to the garage and put a new starter motor on all was good to start again and then I parked up then went to start it and it just clicked again!! Any ideas what it could be

 

Two things come to mind. Either a bad battery and you charged it up enough driving it to the shop, for it to start at the shop or a bad alternator that's not charging the battery. Well. maybe a third thing. A bad ground